Turbogenerator End Region Research Articles

Loss Distribution in Stator End Region of Turbo-Generator during Asynchronous Operation after Different Excitation Faults

A turbo-generator during asynchronous operation after the excitation fault can absorb lots of reactive power and result in the increase of the leakage flux and losses in the stator end region. In order to study the loss distribution of the stator end structural components during asynchronous operation, this paper presents a method combining the 2-D field-circuit coupled time-stepping finite element model (FCCTSFEM) with the 3-D transient electromagnetic field in the end region of the turbo-generator. The asynchronous processes of the turbo-generator under the open- and short-circuit faults of field winding are calculated by FCCTSFEM, and 3-D transient electromagnetic field and the losses in the stator end region of the turbo-generator are calculated. From the detailed performance evaluations by the 3-D finite-element analysis, the flux densities and loss distributions of the stator end structural components are compared under different excitation faults. The influence of the metal shield material on the flux densities and losses of the stator end region is studied. The variations of the losses in different stator end structural components are revealed along with the conductivity of the metal shield. The results could provide a theoretical basis for improving the asynchronous operating ability of the turbo-generator after the excitation fault.

Influence of Electric Shield Materials on Temperature Distribution in the End Region of a Large Water–Hydrogen–Hydrogen-Cooled Turbogenerator

To investigate the influence of different electric shield materials on the temperature distribution in the turbogenerator end region, a 330-MW water–hydrogen–hydrogen-cooled turbogenerator is considered in this paper. Mathematical and physical models of the three-dimensional (3-D) transient electromagnetic field in the turbogenerator end region are established. The magnetic density distribution and the losses of end parts are obtained with different electric shield materials. The loss values obtained from the 3-D transient electromagnetic field calculations with different electric shield materials are applied to the end parts as heat sources. Pressure and fluid velocity values from flow network calculations are applied to the end region as boundary conditions for the fluid and thermal coupling analysis. In addition, a 3-D fluid and thermal coupling model of the turbogenerator end region is established. The distributions of the surface heat transfer coefficient on the inner and outer surfaces of the electric shield are determined with different electric shield materials. Temperature distributions of the stator-end copper winding, finger plate, clamping plate, and electric shield in the turbogenerator end region are investigated with different electric shield materials. The calculated temperature results for the electric shield are compared with measured values, and the calculated results agree well with the measured values.

Practical model of the axial magnetic field in the end region of large turbo-generators

PurposeThe axial magnetic field occurs in the end-region of large turbo-generators is known to induce hot points or voltages between laminations, that may cause insulation breakdown and thus stator faults.Design/methodology/approachIt is important to dispose of simple methods for estimating the axial flux rapidly with regard to the operating point of the machine.FindingsThe authors provide a practical model of the axial magnetic field based on a simplified vector diagram. The parameters required to build the vector composition of the flux densities are assessed with a limited number of finite element method simulations of the whole end-region of the machine. These simulations were validated by an experimental test on a real turbo-generator. Then the axial flux density was simply estimated for various operating points.Originality/valueThe originality of the paper concerns the practical model of the axial magnetic field based on a simplified vector diagram.

Influence of different underexcited operations on thermal field in the turbogenerator end region with magnetic shield structure

The losses and temperatures of end parts will increase obviously in the turbogenerator end region under underexcited operation. In order to study the influence of different underexcited operations on temperature of end parts in the turbogenerator end region with magnetic shield structure, a turbogenerator is considered as an example in this paper. Three-dimensional transient electromagnetic field of turbogenerator end region is given. The magnetic density distribution of clamping plate and magnetic shield is researched. The losses of end parts and stator end cores from three-dimensional transient electromagnetic field calculation are applied to end region as heat sources under different underexcited operations. Pressure value of fan outlet and velocity values of different inlets from flow network calculations are applied to end region as boundary conditions in the 3-D fluid and thermal coupling analysis model. Further, fluid field and thermal field are calculated under different underexcited operations. The distribution laws of fluid velocity and fluid temperature in the turbogenerator end region are determined. The temperature distribution laws of the stator-end copper windings, press finger, clamping plate, screen plate, magnetic shield, and stator end cores are studied under different underexcited operations. The accuracy of numerical calculation is validated by measured values.

Influence of Magnetic Permeability of the Press Plate on the Loss and Temperature of the End Part in the End Region of a Turbogenerator

Press plates are widely used in the end region of turbogenerators. However, due to the effect of magnetic field leakage from the end region, the eddy current losses of the copper screen and press plate will result in the copper screen and press plate having a high temperature under the rated load condition. In this paper, the influence of the magnetic permeability of the press plate on losses and temperature of the end region is researched in turbogenerators. Three-dimensional (3-D) fluid and thermal mathematic and physical models of the turbogenerator end region are established. Under different magnetic permeability values of the press plate, a 3-D transient electromagnetic field in the turbogenerator end region is calculated, and the obtained losses of the end parts are treated as heat sources. Fluid network equations are calculated, and the obtained fluid velocity and pressure values are applied to the end region as boundary conditions. After solving the fluid and thermal equations, fluid velocity around the surface of the end parts is obtained under the rated load condition. The temperature distribution of the end parts is determined for different magnetic permeability values of the press plate. The calculated temperature results agree well with the test data.

Analysis of complex fluid flow and temperature field in the turbogenerator end region with magnetic shield structure under underexcitation operation

The large electromagnetic losses and high temperature rise under underexcitation operation are the main issues of large turbogenerator design. In order to study the eddy current losses, fluid velocity, and temperature distribution in the turbogenerator end region with magnetic shield structure under underexcitation operation, three-dimensional transient electromagnetic field of a 1250 MW turbogenerator end region is investigated. The losses of end parts and stator end cores (heat source) are obtained under underexcitation operation. Velocity values of different inlets and pressure value of fan outlet (boundary condition) are determined by flow network calculation. Meanwhile, three-dimensional fluid and thermal fields are calculated. The distribution of fluid flow between magnetic shields is obtained. The temperature distribution of end parts and stator end cores in the end region of large turbogenerator is studied under underexcitation operation with 0.9 pf lead. Calculation results are compared with experiment data, which provides a reliable basis for the design and operation of larger turbogenerator.

Numerical analysis of end part temperature in the turbogenerator end region with magnetic shield structure under the different operation conditions

Due to the serious overheating problem of end parts in the large turbogenerator end region, accurate calculation of end-part temperature has become a key design factor. In this paper, 3-D fluid and thermal coupling model in the end region of 1250 MW turbogenerator are given. The loss values gained from 3-D transient electromagnetic field calculation are applied to the solving end region as heat sources. Pressure value of fan outlet and fluid velocities of end region inlets from flow network calculation are applied to the solving end region as boundary conditions in the 3-D fluid and thermal coupling analysis model. The fluid flow and temperature distribution of end parts in the end region of large turbogenerator with magnetic shield structure are studied under the different operation conditions. The distribution of fluid velocity in the ventilation duct of stator end core is obtained. The temperature distribution laws of stator-end copper coils, screen plate, finger plate, press plate, and magnetic shield are researched under the different operation conditions. The location of the highest temperature point in the turbogenerator end region with magnetic shield structure is determined. The accuracy of numerical calculation is validated by experimental measured values.

Assessment of the Stray Flux, Losses, and Temperature Rise in the End Region of a High-Power Turbogenerator Based on a Novel Frequency-Domain Model

The electromagnetic and heat issue is the core of the key problems for large synchronous generators. This paper presents a new method to account for the rotary excitation field of a large synchronous generator using a new 3-D static frequency-domain finite element to solve the end magnetic field and electromagnetic losses via phase transformation. The solution time is significantly reduced. Both magnetic flux leakage and temperature testing of the end structures are conducted. There is good consistency between the theoretical simulation and the experimental results for both magnetic and thermal fields. The regularity of the magnetic and thermal field distributions is studied drawing on the electromagnetic and heat transfer theories.

Numerical calculation of CHTC on end metal parts and flow in end region of a turbogenerator

The convection heat transfer coefficient (CHTC) distribution of surfaces of end metal parts directly affects the temperature distribution of end metal parts. In this study, a large turbogenerator is analysed. To study the CHTC distribution of surfaces of end metal parts in detail, a three-dimensional (3D) fluid and thermal analysis model of whole turbogenerator end region is established. The losses of end metal parts from 3D transient electromagnetic field calculation are provided to end metal parts as heat sources. Pressure values of end-region outlets and fluid velocity of fan outlet from flow network calculation are provided to end region as boundary conditions in the 3D fluid and thermal analysis model. CHTC distribution laws of the surfaces of the clamping plate, finger plate, and copper screen are studied in detail by the finite volume method. The fluid flow and temperature distribution of end metal parts are determined in the end region of the turbogenerator. The calculated results are compared with measured data.

Calculation of Temperature Distribution in End Region of Large Turbogenerator Under Different Cooling Mediums

In order to study the influence of different cooling mediums on the fluid velocity and the temperature distribution of end parts in the turbogenerator end region, a 330-MW turbogenerator is analyzed. Three-dimensional fluid-thermal coupling analysis model of the turbogenerator end region is given. When the different cooling mediums are used, fluid velocity of fan inlet and pressure values of end-region outlet from the flow network calculation are applied to the end region as boundary conditions, and the losses from 3-D transient electromagnetic field calculation are applied to the end parts as heat sources in the fluid-thermal coupling field. The fluid field and temperature field in the turbogenerator end region are calculated using the hydrogen and air as cooling medium, respectively. Fluid velocity and temperature of end parts in the turbogenerator end region are compared when the different cooling mediums are used. When the hydrogen is used as the cooling medium, comparing the calculated temperature results with the test values, the calculated temperature results match well with test values. These will provide a reference for the ventilation cooling design of large turbogenerator.

Erratum to “Influence of Cooling Fluid Parameter on the Fluid Flow and End Part Temperature in End Region of a Large Turbogenerator” [Jun 16 466-476

Erratum to “Influence of Cooling Fluid Parameter on the Fluid Flow and End Part Temperature in End Region of a Large Turbogenerator” [Jun 16 466-476

Influence of Cooling Fluid Parameter on the Fluid Flow and End Part Temperature in End Region of a Large Turbogenerator

In order to study the influence of the cooling fluid parameter on the fluid flow and end part temperature in the end region of the large turbogenerator, a 330-MW water–hydrogen–hydrogen cooled turbogenerator is analyzed. The fluid velocity and pressure values from the flow network calculations are applied to the end region as boundary conditions and the losses obtained from 3-D transient electromagnetic field calculations are applied to the end parts as heat sources in the fluid and thermal coupling analysis. After solving the fluid and thermal equations of fluid–solid conjugated heat transfer, the fluid velocity and end part temperature in the turbogenerator end region are gained under the different cooling fluid parameters. The influence of different fluid velocities and fluid temperatures in the water pipe inlet, and in the fan inlet on the fluid flow and end part temperature in the turbogenerator end region is researched. The calculation results of copper shield temperature are compared with the measured values. The calculation results coincident well with the measured values. These provide the important reference for better cooling turbogenerator end region.

Calculation and analysis of complex fluid flow in the multistage fan of a large turbogenerator end region

In order to study the distributions of complex fluid velocity and fluid pressure in the multistage fan of a large turbogenerator end region, the multistage fan in the 1407 MVA turbogenerator is analyzed. Characteristic curve of pressure and fluid rate of the multistage fan is determined. Static pressure distribution of dynamic and static fan blade surfaces and fluid velocity distribution around dynamic and static fan blade surfaces in the multistage fan are researched. The distribution laws of radial velocity, tangential velocity, and axial velocity between dynamic fan blade and static fan blade are given. The change laws of fluid static pressure and fluid total pressure are analyzed after fluid passes through dynamic and static fan blades. The calculated results match well with measured data. This research can provide an important reference for the optimal design and research of multistage fan in a large turbogenerator.

Research on the Impact of Screen Properties on Eddy Current and Flux in End Region of a Large Air-Cooled Turbo-Generator

Large turbo-generators are an important energy conversion device in power stations. Once a failure occurs in the turbo-generator, it not only affects the reliability of the power system but also causes enormous economic losses. Nowadays, large air-cooled turbo-generators have developed. The safe and steady operation of turbo-generator is important for the electric power system. Leakage magnetic field is a potential hazard in end region of a turbo-generator. Leakage magnetic flux could cause eddy current to be induced in the metal component of end region, which leads to heat generation. In this paper, aiming at the complex end structure of turbo-generator, a three dimensional (3-D) mathematic model used for electromagnetic field calculation in end region of a 150-MW air-cooled turbo-generator is established. Finite element method is used to calculate the 3-D magnetic field in end region of a turbo-generator. Magnetic flux leakage testing is conducted under noload condition. It shows that there is a good agreement between the theoretical simulation and the experimental results. Eddy current loss of end parts is gained based on the electromagnetic induction theory.

Analysis of Three-Dimensional Complex Fluid Flow and Temperature Distribution in the End Region of a Turbogenerator

Distribution of complex fluid flow is an important factor that affects the temperature distribution of the end parts in the end region of a turbogenerator. In this paper, a turbogenerator is considered as an example; the fluid flow velocity and pressure values obtained from flow network calculations are applied to the end region as boundary conditions, and the losses obtained from electromagnetic field calculations are applied to the end region as heat sources in a fluid and thermal coupling field. Furthermore, mathematical and geometric models of 3-D fluid and thermal coupling of the end region are established. The distributions of the complex fluid velocity and fluid temperature in the turbogenerator end region are investigated in detail. Moreover, the temperature distribution of the end parts is determined. Comparison of measurement results of the temperature of the end parts with the corresponding calculation results shows their good agreement.

Calculation and Analysis of the Surface Heat-Transfer Coefficient and Temperature Fields on the Three-Dimensional Complex End Windings of a Large Turbogenerator

With increased turbogenerator capacity and electromagnetic load, overheating of the complex end parts has become one of the main problems affecting safe and stable turbogenerator operation. In this research, a flow network was built representing the structural and ventilation characteristics of a 330-MW turbogenerator. The fan inlet velocity and pressures (boundary conditions) of each end-region outlet were obtained by the flow network method. The 3-D transient electromagnetic field in the turbogenerator end was calculated, and the eddy current losses (heat sources) of the end parts were obtained by the finite-element method. To study the surface heat-transfer coefficient distribution on the stator-end winding surface, fluid and thermal mathematical and geometric models of the whole turbogenerator end region were given. Using the finite-volume method, the surface heat-transfer coefficient distribution on the complex 3-D stator-end winding surface, fluid-flow distribution, and temperature distribution of the end parts were investigated under rated-load conditions. The calculated temperature results match well with measured data. This research can provide a theoretical basis for calculating the heat-transfer coefficients of the outer surfaces of large turbogenerators.

Numerical Calculation and Analysis of Three-Dimensional Transient Electromagnetic Field in the End Region of Large Water–Hydrogen–Hydrogen Cooled Turbogenerator

Due to the complexity of the structures and magnetic field distribution in the end region of large turbogenerators, using a 330-MW water-hydrogen-hydrogen cooled turbogenerator as an example, the 3-D mathematical and geometry models of the nonlinear transient eddy current field were given. Taking the nonlinearity of the core material and the influences of noncontact between the copper screen and the clamping plate, as well as the shape of stator end windings into consideration, the 3-D transient electromagnetic field was calculated, and the losses of different metal parts were obtained by the finite-element method. The calculated power losses were applied to the thermal field as heat sources. Temperatures of the copper screen were gained. The calculated results of copper screen were well coincident with the test data. Hence, the calculated results are accurate, and the method of calculation is effective.

Influence of Copper Shield Structure on 3-D Electromagnetic Field, Fluid and Temperature Fields in End Region of Large Turbogenerator

A new kind of the copper shield structure called the empty solid copper shield structure (ESCSS) in the large turbogenerator is proposed in this paper. Based on the complex structure characteristics of a 330-MW water-hydrogen-hydrogen cooled turbogenerator, the flow network within a half of the generator is established, and the total flow rate, pressure, flow rates (boundary conditions) of the various ventilation ducts and the chambers in the generator are separately obtained after solving the equations of the flow network when the traditional copper shield structure and the ESCSS are adopted. The 3-D transient electromagnetic field of the generator end region is calculated by using the time-stepping FEM, and the electromagnetic loss distributions (heat sources) are determined separately. Then, the fluid and thermal analysis model for the whole end region is established. Through numerical calculating, the whole end region 3-D fluid and temperature distributions are obtained separately. The results show that the new copper shield structure makes the copper shield temperature much lower. Meanwhile, the copper shield material is saved. The obtained conclusions may provide useful reference for the optimal design and research of the large turbogenerator.

Influence of clamping plate permeability and metal screen structures on three-dimensional magnetic field and eddy current loss in end region of a turbo-generator by numerical analysis

A significant problem of turbogenerators on complex end structures is overheating of local parts caused by end losses in the end region. Therefore, it is important to investigate the 3-D magnetic field and eddy current loss in the end. In end region of operating large turbogenerator at thermal power plants, magnetic leakage field distribution is complex. In this paper, a 3-D mathematical model used for the calculation of the electromagnetic field in the end region of large turbo-generators is given. The influence of spatial locations of end structures, the actual shape and material of end windings, clamping plate, and copper screen are considered. Adopting the time–step finite element (FE) method and taking the nonlinear characteristics of the core into consideration, a 3-D transient magnetic field is calculated. The objective of this paper is to investigate the influence of clamping plate permeability and metal screen structures on 3-D electromagnetic field distribution and eddy current loss in end region of a turbo-generator. To reduce the temperature of copper screen, a hollow metal screen is proposed. The eddy current loss, which is gained from the 3D transient magnetic field, is used as heat source for the thermal field of end region. The calculated temperatures are compared with test data.

Influence of Copper Screen Thickness on Three-Dimensional Electromagnetic Field and Eddy Current Losses of Metal Parts in End Region of Large Water-Hydrogen–Hydrogen-Cooled Turbogenerator

Aiming at the complexity of the structure in the end region of large turbogenerators, 3-D mathematical and physical models of nonlinear transient eddy current field are given by taking a 330-MW water-hydrogen-hydrogen-cooled turbogenerator for example. Both nonlinearity of <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">B</i> - <i xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">H</i> curve and noncontact structure between the copper screen and press plate, as well as the evolvent of stator end windings, were taken into consideration. When the copper screen thickness is different in the end region of the generator, 3-D transient electromagnetic field and losses of metal parts were calculated under no-load and rated-load conditions by finite-element method. The metal part losses, which were obtained from transient electromagnetic field, were applied to the thermal field as heat sources. Temperatures of copper screen were gained after the thermal field was calculated in the end region. The calculated results coincide well with the measured data.